Studies have been made on artificial lungs as supporting means in open-heart surgery or supporting means of respiration over a long period of time. Thus, there have been developed artificial lungs of various types. It is generally needed to impart antithrombotic properties to these artificial lungs so as to prevent blood coagulation.
To impart the antithrombotic properties, for example, U.S. Pat. No. 6,200,588 discloses a method of improving the antithrombotic properties by coating the surface of a part of a medical instrument to be contacted with blood with an ionic complex derived from: a quaternary alkylammonium salt having from 24 to 32 carbon atoms in total; and heparin or a heparin derivative. However, if the method disclosed therein is applied to the production of an artificial lung, there arises a problem that the artificial lung thus obtained frequently suffers from thrombus formation when used for a long time.
It is generally required that artificial lungs have characteristics such as not undergoing so-called wet lung (i.e., a phenomenon wherein vapor condenses and spreads out over the membrane surface in the side to be contacted with blood, thereby lessening the gas exchange area) and not hematologically activating complements. However, polyurethane, polyvinyl chloride and polycarbonate disclosed by U.S. Pat. No. 6,200,588 as medical instrument bases are insufficient in the above-described characteristics. Thus, the medical instruments disclosed by U.S. Pat. No. 6,200,588 are insufficient in the above-described characteristics as artificial lungs.